The present invention relates to a hydrocarbon conversion and more particularly to a process for producing gasolin having a high octane number and/or aromatic hydrocarbons by contacting a feed stock containing aliphatic hydrocarbon(s) of 1 to 12 carbon atoms with a zeolite catalyst at an elevated temperature.
In petroleum refineries, cracked gases comprising C.sub.1 to C.sub.4 paraffins and/or olefins are by-produced in large quantities from fluid catalytic cracking unit, thermal cracking unit or hydrocracking unit. These gases are usually consumed as fuel in those refineries or for domestic use. But, the development of use having an enhanced added value is desired.
Further, in producing ethylene and propylene by subjecting a petroleum distillate such as naphtha to a thermal cracking treatment in the presence of steam, a considerable amount of thermal-cracked gasoline is produced. Since this thermal-cracked gasoline contains a large amount of diolefins, it tends to polymerize during storage and form a large amount of gum, so it is desired to develop an effective method for removing the diolefins.
On the other hand, light straight-run naphtha from a distillation column is usually employed as a blend with gasoline, but a novel aromatization method has been desired because of a low octane number. Medium and heavy naphtha distillate from a distillation column is introduced into a reforming unit to produce reformed gasoline. But, the reformed gasoline contains large amounts of saturated aliphatic hydrocarbons, including those of C.sub.5 and C.sub.6, which are a cause of reduced octane number of products.
As a method for effectively utilizing C.sub.2 to C.sub.5 olefin gas contained in the above cracked gas, there is a polymer gasoline method or OTG reaction (Olefin-to-Gasoline), in which the said olefin gas is low-polymerized for conversion into gasoline. A solid acid is usually employed as catalyst, typical of which is a catalyst comprising diatomaceous earth or quartz sand and phosphoric acid adsorptively immobilized thereon. In this case, it is necessary that the operation for adsorptively immobilizing phosphoric acid should be done frequently because phosphoric acid is washed away quickly.
It is also known to use zeolite as catalyst. Especially, zeolites with pores each comprising a ten- or twelve-membered oxygen ring, such as ZSM-5, ZSM-11, mordenite, Y type zeolite and faujasite, exhibit after dealkalization a superior OTG reaction activity. For example, it is disclosed in Japanese Patent Laid Open No. 103292/1981 that aromatic hydrocarbons can be obtained in high yield by using as catalyst a zeolite having a high silica/alumina ratio such as ZSM-5 or ZSM-11. And it is disclosed in Japanese Patent Laid Open No. 24835/1979 that such zeolite catalyst is also effective for the aromatization of diolefins contained in thermal-cracked gasoline. Further, it is disclosed in Japanese Patent Publication No. 42639/1981 and Laid Open No. 93918/1982 that catalysts comprising such zeolites and various metals supported thereon permit conversion of not only unsaturated aliphatic hydrocarbons but also saturated aliphatic hydrocarbons into aromatic hydrocarbons.
However, in OTG reaction and aromatization using those zeolite catalysts, there occurs a rapid deterioration of catalytic activity caused by deposition of coke, so it is necessary to frequently perform the operation for catalyst regeneration by air calcination.